* Corresponding authors

^a Department of Chemistry, Jadavpur University, Kolkata 700032, India
E-mail: agayenju@yahoo.com, arup.gayen@jadavpuruniversity.in
Fax: +91-33-2414-6223
Tel: +91-33-2457-2767

^b Department of Physics, Jadavpur University, Kolkata 700032, India

^c Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata 700106, India

^d Surface Engineering Division, CSIR – National Aerospace Laboratories, Bengaluru, India

^e Department of Chemistry and Centre of Nanotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India

^f Department of Chemistry, Visva-Bharati, Santiniketan 731235, India
E-mail: mdmotin.seikh@visva-bharati.ac.in
Fax: +91-3463-262672
Tel: +91-9933052194